In order to have a good performance in putting the ball to hole, the player's eyes 33 are to be aligned exactly on the top of the putting line so that the player can see the ball and centre alignment mark 4 (or line) on putter (match with putting line 31) and target hole 32 to be all in one line. Otherwise the ball putted goes to the wrong direction not intended by player due to misalignment. However we can not find any suitable putter to fulfill these performances in the market.
Usually golf coaches ask golf beginners to make another ball drop from the eyes to hit the aligned ball to be put in order to find whether the player has a good alignment.